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.TH LISTEN 3XNET "Jun 10, 2002"
.SH NAME
listen \- listen for socket connections and limit the queue of incoming
connections
.SH SYNOPSIS
.LP
.nf
\fBcc\fR [ \fIflag\fR ... ] \fIfile\fR ... \fB-lxnet\fR [ \fIlibrary\fR ... ]
#include <sys/socket.h>

\fBint\fR \fBlisten\fR(\fBint\fR \fIsocket\fR, \fBint\fR \fIbacklog\fR);
.fi

.SH DESCRIPTION
.sp
.LP
The \fBlisten()\fR function marks a connection-mode socket, specified by the
\fIsocket\fR argument, as accepting connections, and limits the number of
outstanding connections in the socket's listen queue to the value specified by
the \fIbacklog\fR argument.
.sp
.LP
If \fBlisten()\fR is called with a \fIbacklog\fR argument value that is less
than 0, the function sets the length of the socket's listen queue to 0.
.sp
.LP
The implementation may include incomplete connections in the queue subject to
the queue limit. The implementation may also increase the specified queue limit
internally if it includes such incomplete connections in the queue subject to
this limit.
.sp
.LP
Implementations may limit the length of the socket's listen queue.  If
\fIbacklog\fR exceeds the implementation-dependent maximum queue length, the
length of the socket's listen queue will be set to the maximum supported value.
.sp
.LP
The socket in use may require the process to have appropriate privileges to use
the \fBlisten()\fR function.
.SH RETURN VALUES
.sp
.LP
Upon successful completions, \fBlisten()\fR returns 0.  Otherwise, \(mi1 is
returned and \fBerrno\fR is set to indicate the error.
.SH ERRORS
.sp
.LP
The \fBlisten()\fR function will fail if:
.sp
.ne 2
.na
\fB\fBEBADF\fR\fR
.ad
.RS 16n
The \fIsocket\fR argument is not a valid file descriptor.
.RE

.sp
.ne 2
.na
\fB\fBEDESTADDRREQ\fR\fR
.ad
.RS 16n
The socket is not bound to a local address, and the protocol does not support
listening on an unbound socket.
.RE

.sp
.ne 2
.na
\fB\fBEINVAL\fR\fR
.ad
.RS 16n
The \fIsocket\fR is already connected.
.RE

.sp
.ne 2
.na
\fB\fBENOTSOCK\fR\fR
.ad
.RS 16n
The \fIsocket\fR argument does not refer to a socket.
.RE

.sp
.ne 2
.na
\fB\fBEOPNOTSUPP\fR\fR
.ad
.RS 16n
The socket protocol does not support \fBlisten()\fR.
.RE

.sp
.LP
The \fBlisten()\fR function may fail if:
.sp
.ne 2
.na
\fB\fBEACCES\fR\fR
.ad
.RS 11n
The calling process does not have the appropriate privileges.
.RE

.sp
.ne 2
.na
\fB\fBEINVAL\fR\fR
.ad
.RS 11n
The \fIsocket\fR has been shut down.
.RE

.sp
.ne 2
.na
\fB\fBENOBUFS\fR\fR
.ad
.RS 11n
Insufficient resources are available in the system to complete the call.
.RE

.SH ATTRIBUTES
.sp
.LP
See \fBattributes\fR(7) for descriptions of the following attributes:
.sp

.sp
.TS
box;
c | c
l | l .
ATTRIBUTE TYPE	ATTRIBUTE VALUE
_
Interface Stability	Standard
_
MT-Level	MT-Safe
.TE

.SH SEE ALSO
.sp
.LP
.BR accept (3XNET),
.BR connect (3XNET),
.BR socket (3XNET),
.BR attributes (7),
.BR standards (7)
